TreeTableView can't expand/collapse row using keyboard when in cell selection mode

1. Run HelloSimpleTreeTabeView
2. Select a Row with sub rows, use left/right arrow keys will expand and collapse the row.
3. Select 'cell selection' on the button at the top.
4. Repeat the same process, left/right arrow keys move the selection across columns
As far as I can tell the rows can't be expanded/collapsed using the keyboard in cell selection mode